The present invention is concerned with a discharge valve of novel type for use in a hydraulic circuit.
Many types of discharge valves are known which are particularly used in mine props. Such a valve is adapted to establish a leakage in a fluid circuit where the fluid is compressed beyond a determined pressure limit.
In certain known discharge valves, the fluid pressure is applied to as to raise from its seat a valve member by acting against an opposing spring. In the absence of pressure, the spring maintains the said member very strongly against its seat. This permanent contact ensures conservation of the surfaces. Moreover, the spring is always compressed and it happens frequently that the pressure limit or calibration of the valve varies according to the shelf life. Indeed when the fluid pressure is lower than this calibration the force of application of the valve member on its seat varies inversely to the fluid pressure such that if the calibration is not precise the opening of the valve is very progressive.
In other known valves, the valve member is urged to its seat by a reserve of compressed gas. There again the contiguous surfaces are constantly compressed, and one cannot control the valve of calibration which necessitates storage of a large number of valves of different kinds.
The present invention has for its object the avoiding of these inconveniences by providing a valve in which the forces applied to the contacting surfaces at the edge of the seat remain practically nil when the fluid circuit is not under pressure. This valve has moreover a more precise calibration value which is controllable.
A discharge valve according to the invention comprises a body in which a first fluid-tight chamber is adapted to be put into communication with a pressurised fluid circuit while a second chamber is provided with at least one orifice permitting fluid to escape freely, and a valve member adapted to rest on a seat to separate these chambers or to place them in mutual communication, the valve being characterised in that the valve member is urged against its seat on the first chamber side, the seat being disposed on a slidable barrel disposed adjacent a spring so that in the absence of pressure in the first chamber the spring has practically no effect, and an abutment fixed to the body being provided so as to contact the valve body when the latter is on its seat and slides with the barrel, an increase of fluid pressure in the first chamber producing the following effects:
If the pressure remains lower than the calibration value of the valve, the valve member is applied against the seat by the fluid with a force proportional to this pressure when the barrel slides and compresses the spring, PA1 if the pressure is above the calibration value of the valve, the valve member contacts the abutment when the barrel slides by compressing the spring so that the seat is spaced from the valve member.
According to a supplementary characteristic of the invention, the body of the valve comprises a central bore, whereof one end is closed by a cap having an integral coaxial stem which slides in the central bore of a cylinder laterally extending the barrel carrying the seat, the cap being provided with an axial through hole to permit placing in communication the pressurised fluid circuit and the first chamber delimited in the interior of the cylinder by the end of the stem, a seal being provided between the cylindrical surface of the stem and the cylinder bore.
According to a supplementary characteristic of the invention the first chamber encloses a small helical spring constantly compressed between the valve member and the end of the stem to urge the valve member in the direction of its seat, this small spring being much less powerful than the barrel return spring.
According to a supplementary characteristic of the invention the valve membe is constituted by a ball and the seat is constituted by a truncated bore.
According to a modification, the valve member is constituted by a truncated finger and the seat is constituted by the orifice of a hole in the barrel.
According to another modification, the valve member has at its end a plane annular surface adapted to abut against the face of a circular boss constituting the seat.
According to a supplementary characteristic of the invention the second chamber is constituted by the remaining free volume of the central bore of the valve body beyond the barrel on which the seat is located.
According to a supplementary characteristic of the invention the return spring of the barrel is constituted by a helical spring, whereof one end abuts a shoulder of the body, at the end of the central bore, and whereof the other end abuts the slidable barrel.
According to a supplementary characteristic of the invention, the other end of the central bore of the valve body is also closed by a cap in the center of which is fixed a rod extending axially into the bore and adapted to engage with substantial play inside the seat on the sliding barrel, and whereof the free end constitutes an abutment for the valve member. This abutment can be plane, round, sharp, or any appropriate form to suit the type of valve member.
According to a supplementary characteristic of the invention, this rod is screw engaged in a bore of the cap, and it can be used to control the calibration value of the valve by being screwed in one direction or the other, which varies the longitudinal position of its free end.